Printing telegraph system



June 5, 1934. G, VERNAM ET AL 1,961,407

PRINTING TELEGRAPH SYSTEM Filed Dc. 20, 1930 INVENTORS A B) W g 4 iATTORNEY mally closed loop. The repeaters may be un-,

Patented June 5, 1934 UNITED STATES PATENT ()FFICE A. Locke, Glenwood,signer to American N. Y.; said Vernam as- Telephone and TelegraphCompany, a corporation of New York, and said Locke assignor to BellTelephone Laboratories,

Incorporated, acorporation of New York Application December 20, 1930,Serial No. 503,660

Claims.

This invention relates to switching systems, and more particularly tosuch systems as applied to telegraph circuits, and discloses an exchangesystem applicable prinicipally to the use of printing telegraphequipment, by means of which connections may be established quickly andefficiently for communication purposes between any of a plurality ofsubscribers telegraph stations, and further by means of which such :10connections are to remain thus established for more or less temporaryintervals in accordance with the wishes of the subscribers.

An exchange system of the type above referred to is disclosed in thepatent of G. S.

' Vernam, No. 1,804,548, granted May 12, 1931.

In said prior patent a subscribers station and a central oiiice areconnected thorough a normally open loop, and the subscriber, to initiatea call, may signal the operator by closing the circuit of said loop.Where the distance between the subscriber and the central office isshort, the use of a normally open loop 'is economical. However, when thesubscribers station is removed from the central office by a longdistance, it is more economicaltoiconnect the subscribers circuitthrough a repeater to one channel of an open wire duplex, metallic orcarrier frequency circuit. The usual carrier telegraph repeatersnecessitates a normally closed loop be- 501 tween the. subscribersstation and the first repeater, whereby the operator may signal thesubscriber by opening the subscribers loop.

Accordingly, an object of this invention is to provide a circuitextending between a printing telegraph subscribers station and a centralofiice, which may include one channel of a multi-channel system. Inaccordance with this object, both the central office and subscribersstation are connected to a repeater by a norattended and are adapted toconnect the subscribers circuit to the operators circuit over onechannel of a metallic, carrier or similar system.

Another object of this invention is to provide a signaling arrangementin a circuit extending between a subscribers station and a centraloffice whereby either the operator or the subscriber may signal theother for initiating a call, and whereby the subscriber may notify theoperator when he has completed a conversation.

In accordance with the above and other objects, this invention comprisesa subscribers circuit normally closed and connected through r a repeaterto a central ofiice. The subscriber initiates a call by means of a breakkey, with which he opens the loop for about one second. The opening andsubsequent closing of the loop causes a lamp to light in the centraloffice. Conversely, the operator may call the subscriber by means of asimilar break key thereby starting a buzzer at the subscribers stationwhich may continue to vibrate until the subscriber responds by startinghis motor. As an alternative arrangement, the buzzer may be energizedfor only a brief period.

A feature of this invention resides in a relay circuit for actuating thebuzzer. The relay is provided with a locking arrangement whereby eitherthe relay or the buzzer may be maintained in a deenergized condition.The relay armature is released upon the receipt of a break signal and islocked in this open position until the subscriber responds by startinghis motor. During the time that the relay is locked in its open positionand while the loop is closed, current from the loop is effective toactuate the buzzer. When the relay is in its closed position, however,the actuating means for the buzzer is short-circuited.

Another feature of this invention comprises a switching arrangementwhich permits current to flow normally through a relay which controlsthe operation of a buzzer, but which disconnects this relay from theloop and substitutes a resistance. The resistance is selected to be ofsuch value that the impedence of the line is thesame after thesubscriber has answered as before.

Still another feature of this invention is a switching arrangementwhereby the subscriber may notify the operator that he has completed acall. According to this arrangement the subscriber sends a break signalof about ten seconds duration. Means are provided to prevent theactuation of the buzzer in response to this break signal.

In the accompanying drawing,

Fig. 1 shows a telegraph system embodying one form of the invention; and

Fig. 2 shows a modified form of part of the circuit and apparatus at thesubscribers station of Fig. 1. 4

Referring to Fig. 1 an outlying subscribers station B is connected to acentral office or exchange X. At the substation B, telegraphtransmitting and receiving apparatus, to be described subsequently, areconnected in series with each other to form part of a half duplex loopcircuit 10. Another half duplex circuit at the central oflice X isprovided with jacks R2, L2 and C2, whereby the operators telegraph setor other apparatus may be connected at will to form a part of thecircuit 30. Circuits 10 and 30 are arranged so that during the time thatthe subscribers set is not in use there is a normal fiow of current inthese two circuits.

A connecting circuit 20 provides a link be:

tween the subscribers circuit 10 and the operators circuit 30. Theconnecting circuit 20 transfers impulses or signals from the subscriberscircuit to the operators circuit and Vice versa in such manner thatwhenever a discontinuity occurs in either circuit 10 or 30 the currentin the other circuit will correspondingly be interrupted. The connectingcircuit may be any one of a number of types such as open wire, duplex,metallic or carrier frequency. For the purposes of the presentinvention, connecting circuit 20 will be described as a carrierfrequency circuit, employing one channel for station B and otherchannels for stations A and C respectively.

. In order to convert the half duplex direct current impulses to carrierfrequency currents and conversely, a repeater 11 and a similar repeater12 are provided at the respective terminals of connecting circuit 20.For a disclosure of a type of repeater suitable for the purposes of thepresent invention, reference is made to U. S. Patent No. 1,469,259, toB. P. Hamilton, dated October 2, 1923; and to the Vernam Patent1,804,548 mentioned above.

Subscribers apparatus At the outlying station B is situated thefollowing apparatus: A transmitting distributor 16 operated from a keyboard transmitter 15; a receiving relay 18; a receiving distributor 21actuated by the receiving relay l8 and controlling a set of printermagnets 22; a motor 25 for driving distributors 16 and 21; an alarmdevice 55 responsive to a break signal transmitted by the operator atstation X; a break key 39 for signaling the operator to initiate a call;a disconnect key 35 for signaling the operator to interrupt or terminatea call.

Subscribers circuit When the subscribers set is not in use, the positionof the apparatus is as illustrated in the accompanying drawing. Underthese conditions, the loop circuit 10 is closed and may be traced asfollows: Negative battery 33, repeating apparatus at the station 11,conductor 34, disconnect key 35, contact 36, winding of relay 37,contact 38, switch 51, break key- 39, transmitting distributor 16, brush41, conductor 42, main winding of receiving relay 18 and positivebattery 43.

Connecting circuit The carrier circuit 20 connects the subscribers loop10 with the operators loop 30, which, as described subsequently, isnormally closed. Carrier currents are transmitted in opposite directionsover the line 20, in a manner described in the above identified patentto Hamilton 1,469,259. The result accomplished by the carrier line 20and the repeating apparatus 11 and 12 is that when both loops 10 and 30are closed a current flows through both. When either one of the loops isopen the current is interrupted in both loops.

Apparatus-CentraZ oflice At the exchange X is situated the followingapparatus: A repeater jack R2 for connecting the circuit 20 to anothercarrier frequency circult; a listening jack L2 for connecting theoperators set 74 to the circuit 30; a connecting jack C2 for connectingthe circuit 30 with a direct current loop extending to anothersubscriber. The functions of the jacks R2, L2 and. C2 are substantiallythe same as those of the jacks bearing corresponding referencecharacters in the Vernam Patent 1,804,548 mentioned above. Otherapparatus at the exchange X include a signallight 90 for notifying theoperator that a subscriber wishes to initiate, interrupt or terminate acall; a relay 91 for lighting the lamp 90; a condenser 93 for energizingrelay 91 in response to an interruption in the current in the loop 10;and resistances 94 and 95 determining the period of interruptionnecessary to charge condenser 93 and consequently energize relay 91.

operators circuit The operators loop 30 is normally closed and is tracedas follows: Negative battery 105, repeating apparatus 12, conductor 106,winding of relay 92, non-operated contacts of jacks R2, L2 and C2,resistance 96, conductor 107 and positive battery 108.

Initiation of calls by switchboard operator When the operator at theexchange X desires to signal the outlying station E she inserts the plug75 into the jack L2, thereby connecting her printer set 74 to form apart of the circuit 30. The operator then presses the break key 78thereby transmitting a break signal which may be about one second induration. Breaking of the circuit 30 interrupts correspondingly thecurrent in the subscribers loop 10 and deenergizes relay 37. When theoperator closes the key 78 current again flows through the loop circuit10 but takes a diiferent course than formerly. The path taken by thecurrent after the interruption is as follows: Negative battery 33,repeater 11, conductor 34, contact 36, contact 46, break contact andarmature of relay 47, break contact and spring 38 of relay 37, windingsof relay 47 and 48, switch 51, break key 39, distributor 16, con ductor42, relay 18, and positive battery 43. Thus, the loop 10 includes thewindings of relays 47 and 48, instead of relay 37 as normally. Theoperation of relay 48 closes a circuit for energizing the alarm device55 during such time as the relay 48 remains energized.

In cases where the outlying station B isalways attended, and where it isdesired to continue the operation of the alarm device until theattendant answers, relay 47 may be omitted, and the armature and contactfor that relay may be I short-circuited. This modified form is shown inFig. 2.

It is sometimes desirable, however, that the alarm continue only for ashort interval of time, after the loopcircuit 10 automatically restoresto its normal position. Where such a mode of operation is desired, therestoring relay 47 is employed in the manner shown in Fig. 1. Thepurpose of the relay 47 is to remove the short-circuit from the windingof relay 37, which then reenergizes and breaks the circuit through relay48. To this end, relay 47 is selected to be of the slow operating type,and the armature of relay 47 does not break contact until after relay 40has had sufficient time to actuate the alarm device 55.

To answer, the subscriber through the doublepole double-throw powerswitch 51, thereby starting the motors 25 and 54. Motor 25 drives thebrushes of distributors 16 and 21, while motor 54 drives a generator 56for supplying a biasing current to relay 18. Simultaneously the switch51 short-circuits relays 37, 4'7 and 48 and substitutes a resistance 52in the loop 10 to keep the loop current constant. The subscriber thentransmits a signal, by means of the keyboard transmitter 15, whichnotifies the operator that he has responded to the operators signal bystarting his motor. The operator may then either converse directly withthe subscriber, or connect the subscriber B with another callingsubscriber through one of the jacks R2 or C2, in a manner described inthe aforesaid Vernam patent.

Initiating calls at subscribers station I When the subscriber 13 startsa call he first throws the switch 51 into operative position therebystarting the motors. Then, he operates the break key 39 to interrupt thecurrent in the loop circuits 10 and 30 for a short period-say onesecond.

The effect produced at the exchange X by the break signal transmittedthereto will now be described. Since no plug is inserted in jacks R2, L2or C2 at the exchange X, relay 92 thereat is normally operated over thecircuit traced from negative battery 105, repeating apparatus 12,conductor 106, relay 92, non-operated contacts of jacks R2, L2 and C2,resistance 96, conductor 107 and positive battery 108.

Now, relay 92 controls the circuit for operating relay 91, which in turncontrols the light- 7 ing of lamp 90. Associated with relay 92 are thecondenser 93 and the resistance elements 94 and 95. While relay 92 isoperated no charge can accumulate on condenser 93 since both terminalsthereof are connected to battery 98, one terminal being connecteddirectly thereto through resistance 100, and the other terminal beingconnected thereto through the winding of relay 91 and the front contactand armature of relay 92. When, however, relay 92 releases, as explainedabove, due to the reception of the break signal, the upper terminal ofcondenser 93 will be disconnected from battery 98 at the front contactof relay 92 and in place thereof will be connected to ground through thearmature and back contact of the relay and through resistance elements94 and 95 in parallel. As a result, while relay 92 is released, thecondenser 93 will slowly charge up to the potential of battery 98, sothat if the break signal is transmitted long enough the condenser willbe fully charged to the battery potential when relay 92 is reoperated atthe termination of the break signal. The equivalent resistance ofelements 94 and 95 in parallel is such that for the circuit describedthe condenser 93 will be fully charged in about one-half to one second.

After the termination of the break signal, current again flows throughloops 10 and 30, causing the reenergization of relay 92. The operationof relay 92 reconnects the winding of relay 91 across the terminals ofcondenser 93 so that the condenser discharges through the relay Windingand operates the same momentarily. As soon as relay 91 thus operates itcompletes a locking circuit for itself. This circuit is traced frompositive battery 98 through the winding, front contact and right-handarmature of relay 91 toground 112 through non-operated contacts of. jackL2. Relay 91 upon operating, also connects battery 115 to light the lamp90.

After the lamp 90 has been lighted the operator inserts the plug intothe listening jack L2, communicates with the subscriber B, andestablishes a connection to another subscriber,

.through one of the jacks R2 or C2 in a manner more fully described inthe Vernam patent mentioned above.

To recall the operator If during communication with another subscriber,the subscriber B desires assistance from the operator, he operates thedisconnect keyv 35. The operation of this key opens the loop 10 andconsequently the loop 30 for about eight and one-half seconds, causingthe lamp at the exchange X to light, in a manner to be describedsubsequently. The key 35 is arranged so that the contact 36 releasesafter the contact 45, and conversely recloses before contact 46. A keysuitable for this purpose is described in U. S. Patent 1,155,640, issuedOctober 5, 1915 to G. Brown. Recalling the operator requires a longerbreak signal than the one transmitted to initiate a call. The reason forthe longer duration of the recall signal is that the condenser 93charges more slowly when there is a plug inserted in any one of thejacks R2 or C2. During the time the subscriber B is communicatingwithanother subscriber a plug is inserted in one of the jacks R2 or C2.Under these conditions ground is removed from the resistance 95, so thatthe condenser 93 can be charged only through the resistance 94.

Terminating a call At the conclusion of a call, the subscriber Boperates the key 35, and at approximately the same time shuts off theprinter motors by throwing the switch 51. The operation of the key 35opens the loop 10 and consequently the loop 30 for about eight andone-half seconds, in the same manner as when the subscriber desirestorecall the operator. The contact loremains open for a longer periodthan the contact 36. The purpose of this arrangement is to energizerelay 3'? before the winding of this relay is short-circuited throughthe contacts 46 and 38. Thus, improper operation of the buzzer or alarm55 does not occur whether the power switch be opened before or after theloop is closed. The switchboard operator challenges, and if no responseis received, restores the circuit to its original condition bywithdrawing the plug 75 from the jack L2.

What is claimed is:

1. In a communication system, a signal device, a normally closed circuitadapted to be opened momentarily at a remote point, an actuating devicefor said signal device adapted to be energized by the current in saidcircuit, a relay in said circuit and adapted when energized to rendersaid actuating device inoperative, and means for locking said relay in adeenergized position by shunting the winding thereof following a breakof current in said circuit.

2. In a signaling system, a normally closed loop including a source ofcurrent, an alarm relay connected by means of the loop to said source ofcurrent, normally operated means actuated by the loop current fordisabling the alarm relay, and means responsive to an interruption ofloop current for short-circuiting said disabling means, wherebysubsequent closing of the loop energizes the alarm relay.

3. In a signaling system, a normally closed loop including a source ofcurrent, an alarm relay adapted to be connected by means of the loop tosaid source of current, a control relay normally operated by said sourceof current, said control circuiting the alarm relay and non-operatedcontacts for short-circuiting the control relay, whereby the alarm relayis energized by the source of current in response to the opening andsubsequent closing of the loop.

4. A signaling system comprising a local and a remote station connectedto each other by a normally closed loop, said local station comprising asignal relay, means responsive to an interruption at the remote stationof the loop current and the subsequent closure of the loop circuit forenergizing the signal relay, means for transmitting a signal to theremote station by interrupting the loop current, and means forpreventing the signal relay from becoming energized in response to thesignal transmitted by the local station, said last means comprising adevice for short-circuiting the signal relay.

5. A telegraph exchange system comprising in combination a subscriberstelegraph station, a central office connected thereto by one or morecircuits, and having means for connecting said subscribers station witha similar station, means at the subscribers station and responsive to atemporary break in current at the central oince for operating an alarm,means for breaking and reclosing the circuit at the subscribers stationwhereby to signal the operator, and circuit con trol elements forpreventing energization of the alarm in response to a break signaltransmitted at the subscribers station.

6.- A printing telegraph system comprising a plurality of stationsconnected by a normally closed loop, one of said stations comprising analarm relay adapted to be energized in response to the opening and thesubsequent closing of the loop, a control relay normally included insaid loop circuit and having operated contacts for short-circuiting thealarm relay, a key at said one station for transmitting a break signalto the other station and having means to prevent the energization of thealarm relay before the control relay is reenergized.

7. In a telegraph system, a normally closed circuit including atelegraph set and a relay connected in series, said relay being adaptedto relay having operated contacts for short-- actuate a signal deviceinresponse to a-tem porary discontinuity of the current in said circuit,means for rendering said relay and signal device inoperative, said meanscomprising an impedance element having substantially the same impedanceas the relay, and switching means for simultaneously short-circuitingthe relay and connecting the impedance element in series with thetelegraph set.

8. In a telegraph switching system, in combination, aswitchboard and asubscribers telegraph station, a normally closed loop circuit extendingfrom said station to said switchboard, a signal operating device at saidstation, and a circuit controlling instrumentality at said stationresponsive to a temporary interruption and reclosure of the loop circuitfor serially connecting said signal operating device in said loopcircuit.

9. In a telegraph system, two stations, a communication circuitextending therebetween hav-i ing anormal condition, a device at onestation for changing said normal condition for a brief period of time, arelay at said other stationactuated by changing 'saidnormal conditionfor said brief period of time, a source of current and a condensercontrolled by said relay whereby said condenser is charged when saidcircuit is so changed, a device actuatable by the charge on saidcondenser upon restoration of said relay, said system being furthercharacterized in this, that the connection of an extension circuit tosaid communication circuit at said other station operates means to varythe charging rate of said condenser whereby change of said normalcondition for said brief period of time is insufficient to permit thecharging. of said condenser whereby the device actuatable by the chargeon said condenser discriminates in its response to changes in saidnormal condition for brief periods of time as to whether said extensioncircuit is or is not connected to said line.

10. In a telegraph system, a line, a jack at which said line terminates,a condenser, means to charge said condenser upon interruption of saidline, a device actuatable by said condenser upon reclosure of said line,a plug for insertion in said jack, and a device actuatable by insertionof said plug in said jack to so change the charging rate of saidcondenser that the charge on said condenser is effective or inefiectiveto operate said device upon a given duration of opening said line inaccordance with Whether said plug is or is not inserted in said jack.

GEORGE A. LOCKE. GILBERT S. VERNAM.

